The present invention relates to the manufacture of a fiber-reinforced pressure hose of a type having a fiber reinforcement embedded in the resinous material of the wall of the tubular product or between inner and outer tubular layers and, more particularly, to a method of and an appratus for manufacturing the fiber-reinforced pressure hose of the type referred to above.
The manufacture of a fiber-reinforced pressure hose, such as flexible pipe or flexible hose, has heretofore been carried out by winding reinforcing strands spirally on an outer peripheral surface of an inner tube of natural or synthetic rubber or plastic material to form a reinforcing layer and then extruding the natural or synthetic rubber or plastic material onto the reinforcing layer externally of the inner tube to form an outer tube which is integrally bonded to the inner tube through interstices of the spirally wound reinforcing strands forming the reinforcing layer. In this method of manufacturing the fiber-reinforced, flexible pressure hose, since the reinforcing strands are spirally wound directly on the outer peripheral surface of the inner tube, the spirally wound reinforcing strands tend to impart a tightening force on the inner tube to such an extent that the inner tube is radially inwardly stressed. Adjustment of the tension of the individual reinforcing strands prior to the latter being spirally wound on the inner tube would obviate the possibility of generation of the undesirable tightening force, however, it is very difficult with the method of the type described above.
There is also known another conventional method which substantially eliminates the above described drawback and wherein a fiber-reinforced, flexible pressure hose is manufactured by supplying a plurality of longitudinal reinforcing strands onto an elongated mandrel and in equally spaced relation to each other circumferentially of the mandrel and, simultaneously therewith, winding at least two circumferential reinforcing strands on the mandrel spirally in the opposite directions with each other so as to cross over the longitudinal reinforcing strands, thereby forming a reinforcing layer, drawing the reinforcing layer out of the mandrel, and extruding a natural or synthetic rubber or thermoplastic material internally and externally of the reinforcing layer to form the fiber-reinforced, flexible hose at a point of separation of the reinforcing layer from the leading end of the mandrel in terms of the direction of movement of the reinforcing layer being drawn.
In this conventional method, the reinforcing layer, composed of the longitudinal reinforcing strands and the circumferential reinforcing strands spirally wound around the longitudinal reinforcing strands, is slipped off from the mandrel as it is drawn in a direction away from the mandrel. In order for the reinforcing layer to be withdrawn out of the mandrel, a relatively great drawing force is required to draw the reinforcing layer in the direction away from the mandrel because the spirally wound, circumferential reinforcing strands imposes a tightening force on the longitudinal reinforcing strands thereby pressing the latter tight to the outer peripheral surface of the mandrel.
Moreover, in the conventional method, the reinforcing strands, when oppositely spirally wound onto the longitudinal reinforcing strands on the mandrel, tend to be irregularly displaced and, also, one or more of the longitudinal reinforcing strands tend to be twisted and/or slackened. Therefore, the resultant fiber-reinforced pressure hose manufactured according to the above described conventional method is such that the reinforcing layer embedded in the natural or synthetic rubber or plastic material is not uniformly developed over the entire length of the hose to such an extent that the pressure withstanding performance and the flexibility vary at local points on the length of hose and/or the hose tends to be twisted and/or meandered.